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Alloy-free ophthalmic blocking is a modern method of temporarily mounting a spectacle lens blank onto a holder (block) using an adhesive pad instead of a low-melting-point metal alloy. This process is used before the lens is ground and polished.
read more about alloy free ophthalmic blocking ...The main advantage is environmental and safety improvement. Traditional blocking uses an alloy that contains trace metals. Alloy-free blocking eliminates this metal and the need for heat, creating a cleaner, safer, and more environmentally responsible process for the lab.
The system uses a rigid block and a strong, specialized adhesive pad. The pad sticks firmly to the lens and the block. The lens is held securely during surfacing, and afterward, the pad is simply peeled off and discarded.
Traditional blocking uses heat to melt and apply a metal compound, requiring a specialized heating and cooling system. Alloy-free blocking uses room-temperature pressure to bond the adhesive pad, simplifying the blocking and deblocking process.
Adhesive pads provide sufficient structural integrity for most modern lens materials. The pads are engineered to be strong enough to withstand the forces of high-speed grinding without allowing the lens to slip, making sure the final prescription is accurate.
No, alloy blocking is sometimes still used for very thick or unusual glass lenses, but alloy-free is the standard for most plastic lenses.
No, high-quality adhesive pads are designed to peel off cleanly without leaving any residue on the lens coating.
Adhesive pads are designed for a secure grip, but slippage can occur if the lens is not cleaned properly before the pad is applied.
Alloy-free blocking is environmentally safer and prevents "thermal shock" to delicate lens coatings. If your lenses have "crazing" (fine cracks), they may have been blocked using traditional hot-alloy methods. Return them to your provider for a coating warranty check.
The Vision Council. Sustainable Lab Practices (thevisioncouncil.org). 2024.
Review of Optometry. Coating Damage in the Lab (reviewofoptometry.com). 2023.
ABDO. Lens Surfacing and Finishing (abdo.org.uk). 2024.
Optical Laboratory Association. Surfacing Guide (ola-labs.org). 2024.